Well, thanks all for the replies and encouragement. I will exercise and cut calories, if only to prove to myself and others that I did do something to improve my situation. Even if the outcome is meaningless.
Well at least you have your reason, that being "to improve your situation" - to motivate yourself more you may want to expand upon what you mean by improving your situation. There's also the fact you want to prove to yourself, and not just to others. Doesn't this slightly contradict the idea of the outcome being meaningless?